This sounds like a cryptic clue for a crossword!

An eye doctor can be called an optician, so the word 'opt' would be an abbreviation, and is a word in its own right! Maybe this is the word required for the crossword?

There are numerous official abbreviations for all the various professional medical qualifications of eye doctors, none of which appear to be simply 'Opt' ! Furthermore, there is no single or commonly used abbreviation for an eye doctor. So opt for opt. It seems the better option.